Computing devices, such as notebook computers, mobile communication devices, and portable entertainment devices (such as handheld video game devices, multimedia players, and the like) have user-interface devices that facilitate interaction between the user and the computing device. One type of user-interface device that has become common is a touch-sensor pad (also known as a “touchpad”). A touchpad replicates mouse X/Y movement by using two defined axes, which contain a collection of sensor elements that detect the position of a conductive object such as a finger. Mouse right/left button clicks can be replicated by electromechanical switches, located in the vicinity of the touchpad, or by tapping commands on the touchpad itself. The touchpad provides a user-interface device for performing such functions as positioning a cursor and selecting an item on a display.
One type of touchpad operates by way of capacitance sensing utilizing capacitance sensors. The capacitance detected by a capacitance sensor changes as a function of the proximity of a conductive object to the sensor. The conductive object can be, for example, a stylus or a user's finger. In a touch-sensor device, a change in capacitance detected by each sensor in the X and Y dimensions of the sensor array, due to the proximity or movement of a conductive object, can be measured by a variety of methods, such as with self-capacitance or mutual-capacitance sensing techniques. Regardless of the method, usually an electrical signal representative of the capacitance detected by each capacitance sensor is processed by a processing device, which in turn converts these electrical signals into numeric values representative of the position of the conductive object in relation to the touch-sensor pad in the X and Y dimensions. A transparent touch screen, touch-sensor strip, slider, or button operates on the same capacitance-sensing principle.